Apis florea drone flight: longevity and flight performance

Apis florea drone flight: longevity and flight performance

Apis florea drone flight: longevity and flight performance Ninat Buawangpang, Prachaval Sukumalanand, Michael Burgett To cite this version: Ninat Buawangpang, Prachaval Sukumalanand, Michael Burgett. Apis florea drone flight: longevity and flight performance. Apidologie, Springer Verlag, 2009, 40 (1), pp.20-25. HAL Id: hal-00891984 https://hal.archives-ouvertes.fr/hal-00891984 Submitted on 1 Jan 2009 HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Apidologie 40 (2009) 20–25 Available online at: c  INRA/DIB-AGIB/ EDP Sciences, 2008 www.apidologie.org DOI: 10.1051/apido:2008059 Original article Apis florea drone flight: longevity and flight performance* Ninat Buawangpang1 , Prachaval Sukumalanand1 , Michael Burgett2 1 Faculty of Agriculture, Department of Entomology, Chiang Mai University, Chiang Mai, 50200, Thailand 2 Department of Horticulture, Oregon State University, Corvallis, OR 97331, USA Received 17 May 2008 – Revised 8 September 2008 – Accepted 30 September 2008 Abstract – Mating flight records are presented for males (drones) of the Asian dwarf honeybee species Apis florea. These include observations on longevity, mortality and inclusive flight records for a cohort of known-aged males. Averages for flight performance show the flights/lifetime to be 15.3 (± 11.8 SD); the number of flight days, 9.1 (± 6.5 SD) and a drone mating flight lasting ca. 31 min (± 9 min, 27 s SD). For a smaller group of known-aged males, for which complete daily flight performance was recorded for all days of flight, the mean summed flight time was 6 h 38 min (± 5 h 53 min SD). Longevity and mortality data show the average age for commencement of flight to be 5.6 days (± 1.3 SD) and the mean age for the final flight to be 15.6 days (± 9.2 SD), providing an average reproductive flight window of 10 days. These observations for A. florea male longevity and mortality are significantly shorter than those reported for the western honeybee (Apis mellifera L.) as observed in temperate climates of North America. Apis florea / drone / longevity / flight performance 1. INTRODUCTION A recent editorial discussed the paucity of basic research in the area of honeybee drone biology and life history (Koeniger, 2005). This reinforces a long-standing neglect in studies of reproductive flight performance and longevity for male honeybees, most especially for the sympatric Asian honeybee species in the genus Apis. As male honeybees contribute to the overall genetic fitness as much as female re- productives (queens), further studies on male honeybees can contribute much to a more complete understanding of reproductive fit- ness.

From a worldwide perspective, longevity and mortality dynamics are best known for drones of the western honeybee species A. mellifera L. (Page and Peng, 2001; Rueppell et al., 2005). For male reproductive flight dy- namics of Asian Apis species, only the cir- Corresponding author: M. Burgett, burgettm@hort.oregonstate.edu * Manuscript editor: Peter Rosenkranz cadian flight periods for seven Apis species have been examined in any detail (Koeniger and Koeniger, 2000; Otis et al., 2000; Rinderer et al., 1993). A good general review of the life histories of the known Asian honeybee species is to be found in Oldroyd and Wongsiri (2006). Somewhat more expansive studies of drone flight parameters have been reported for A. flo- rea Fabricius and Apis cerana Fabricius; i.e., average length of reproductive flight, the inter- flight period in the colony and the daily flight period (Burgett and Titayavan, 2005; Burgett et al., 2007).

How long male honeybees live and com- prehensive aspects of their flight performance are questions that need addressing for a more complete understanding of their reproductive behavior especially in geographic areas where sympatry occurs. Mortality factors for male honeybee reproductive flight include preda- tion, mis-orientation, exhaustion (Page and Peng, 2001) and the effects of physiological senescence. Longevity of honeybee males is best studied in A. mellifera, where numerous Article published by EDP Sciences

Apis florea drone flight 21 reports give average life spans of 20 to 40 days (Fukuda and Ohtani, 1977; Winston 1987). A maximum life span of 59 days was reported by Howell and Usinger (1933). We are unaware of any comparable longevity studies for drones of Asian Apis. Apis florea Fabricius, commonly known as the dwarf or small honeybee, is one of two species of dwarf honeybees found in South- east Asia. It builds an exposed single comb nest most frequently in a shaded location (Akratanakul, 1977; Seeley et al., 1982). In northern Thailand during the dry winter sea- son, the average A. florea colony occupies a comb area of 490 cm2 , contains 5000 adult workers, 35 adult drones, 215 immature drone stadia, a single female reproductive and 7 re- productive queen cells (Burgett and Titayavan, 2004).

We report here the results of a study of A. florea male flight dynamics and longevity us- ing a cohort of known-aged drones as observed in northern Thailand during the dry winter pe- riod. 2. METHODS All drone flight observations took place on the Chiang Mai University campus in northern Thai- land during the months of February, March and April, 2007, a period when A. florea colonies are actively supporting immature and adult drone pop- ulations. To obtain drones of known age, brood combs possessing pupal drones were incubated in vitro at 34 ◦ C and a RH of ca. 75%. Emerg- ing drones were harvested at 24 h intervals re- sulting in a population of 42 known-aged males which were introduced into an active A. florea colony that had been transferred to the Chiang Mai University campus and placed in a shaded envi- ronment ca. 1.5 m above ground suspended be- tween two poles. To identify individual drones, the males were marked with numbered, colored tags (Opalithplättchen, Chr. Graze KG, Stuttgart, Ger- many). Two trials were conducted over a 60 day period. Trial 1, with 13 marked drones, took place during the period 21 Feb through 11 March and Trial 2, with 29 marked drones, was conducted dur- ing the period 12 March through 20 April. To ob- serve drone flight, two experienced observers vi- sually scanned the comb surface for the presence of drones. Departing drones would most frequently exit the colony from the top portion of the comb. Returning drones were seen to land anywhere on the worker bee curtain covering the comb. Observa- tions began in the early afternoons 15 min prior to anticipated drone flight and continued until the fi- nal return of a marked drone in the mid-afternoon. For the 60 day observational period, drones flew on 57 days; near the end of the observational period in April, traditionally a month with extreme high daytime temperature, three days were character- ized by excessive high temperatures (≥ 40 ◦ C) and hazy conditions that precluded drone flight from the colony. As no apparent differences were seen in any measured parameter between the two trials, drone flight data from both trials have been combined. Afternoon drone flight was observed daily for the entire circadian flight period until the disap- pearance of the final marked drone(s) at the end of the study periods. Drone mortality was assigned as the failure of a male to return from a final ob- served flight. Individual drone flights were recorded to the h-min-sec Thai standard time (GMT + 7 h). For 20 of the 42 known-aged drones, complete flight records were obtained. A complete flight record is the observation of all exits and returns to the colony until the final disappearance of the drone. For the remaining 22 drones, an occasional egress or return flight was not observed. However, for all 42 drones, data concerning age at first flight, age at last flight, total number of flight days and to- tal number of mating flights were recorded. Flight times were corrected to the solar azimuth time ac- cording to the methodology described by Otis et al. (2000).

3. RESULTS 3.1. Flight length Observed drone flights were separated into orientation flights lasting < 10 min and mating flights lasting ≥ 10 min. The average length of an A. florea drone mating flight was 31 min 4 s (± 9 min 27 s SD, n = 481). The mean flight time for the shorter orientation flights was 4 min 31 s (± 2 min 30 s SD, n = 98). 3.2. Circadian flight period The earliest time a drone commenced flight was 12:13 (solar azimuth time) and the latest

22 N. Buawangpang et al. Table I. Apis florea vs. A. mellifera drone flight. Total lifetime flights, total days of flight, age at first flight, and age at last flight. (A. florea data n = 42 |). A. florea A. mellifera1 Total lifetime flights 15.3 ± 11.8 {1 – 56} ? {mean, SD, range} Total flight days 9.1 ± 6.5 {1 – 27} 13.6 ± 9.7 {1 – 38} {mean, SD, range} Age at 1st flight (days) 5.6 ± 1.3 {3 – 8} 11.1 ± 4.8 {5 – 29} {mean, SD, range} Age at final flight (days) 15.6 ± 9.2 {6 – 41} 29.9 ± 10.7 {7 – 54} {mean, SD, range} 1 Data from Rueppell et al., 2005. return flight was 16:10, a circadian flight pe- riod just slightly less than four hours. 3.3. Drone age at first and last flight The earliest initiation of drone flight was 3 days old. The oldest age for a drone to inau- gurate flight was 8 days. The mean age for first flight was 5.6 days (± 1.3 SD) and the mean age for final flight was 15.6 days (± 9.2 SD) with a range of 6 to 41 days (Tab. I). This results in an average reproductive flight win- dow of 10 days, following the initiation of first flight.

3.4. Total flight days and total lifetime flights The mean number of flight days was 9.1 (± 6.5 SD), with a range of 1 to 27 days. The average number of total lifetime mating flights was 15.3 (± 11.8 SD) with a range of 1 to 56 flights (Tab. I and Fig. 1). 3.5. Summed flight time For the cohort of 20 males for which com- plete flight records were obtained, the mean summed flight time was 6 h 38 min 20 s (± 5 h 52 min 51 s SD). This includes both orienta- tion flights and mating flights (Tab. II). 3.6. Statistical analysis Standard regression analysis was applied to the following variables: (1) drone age at first flight vs. total number of flight days, (2) drone age at first flight vs. total number of mating flights, and (3) drone age at first flight vs. age at last flight. For these three conditions no sig- nificant correlations were shown. High signif- icance was shown for the variables total num- ber of flight days vs. total days available for flight (R2 = 0.93, P < 0.001) and total life time flights vs. total number of flight days (R2 = 0.93, P < 0.05). 4. DISCUSSION When comparing the observations of A. flo- rea drones to the temperate A. mellifera model, obvious similarities and differences are seen. The average A. florea mating flight is some- what longer (by 3 min 28 s) than that reported by Burgett and Titayavan (2005), however the data base we report here is significantly larger than their 2005 report (481 vs. 73 observed flights). The length of an average male mating flight is comparable for both A. florea and A. mellifera, vin. 30 min (Burgett and Titayavan, 2005; Howell and Usinger, 1933; Witherell, 1972). Comparative observations on A. cerana drone flight (Burgett et al., 2007) revealed an average drone flight time of ca. 16 min which is only about half of the average for A. flo- rea and A. mellifera. The average A. florea

Apis florea drone flight 23 Figure 1. Apis florea drone flight record. Lifespan and flight activity of 42 known-aged drones. Each row represents a single drone with age (days) on the x-axis coded in gray for no flight activity and black for flight activity. Drones are sorted according to their lifespan and then age at initiation of flight. queen mating flight is reported as 18–30 min (Koeniger et al., 1989) which corresponds closely to the average A. florea drone flight du- ration. Our observations on male longevity, age at initiation of first flight, and total flight days are much reduced for A. florea in compari- son with those reported for A. mellifera see (Tab. I). Similar observations for A. cerana are not known to exist. Our reported flight win- dow of ca. 4 h (1213 h to 1610 h) is somewhat longer than that previously reported (Burgett and Titayavan, 2005), vin. 1300 h to 1530 h, however, in the present study, 98% of all drone exit flights took place after 13:00 and 93% of all return flights occurred before 15:30 h, therefore the preponderance of male reproduc- tive flight did occur within a 2.5 h window. A comprehensive study of A. mellifera drones Rueppell et al. (2005) reported a mean age for initiation of first flight to be 11.1 days; this compares to our observation of a mean age of 5.6 days for A. florea. They reported a mean lifespan for A. mellifera drones of Table II. Apis florea drone flight: summed flight time for drones with complete flight records and to- tal lifetime flights (n = 20 |).

Total flight Total # lifetime time flights Mean 6 h 38 min 20 s 14.8 S.D. 5 h 52 min 51 s 11.7 Range high 16 h 51 min 19 s 39 low 0 h 7 min 37 s 1 29.9 days, while our data for A. florea show an average lifespan of 15.6 days, with a range of 6 to 41 days. This range breadth for A. florea male longevity (see Fig. 1) displays a dramatic intraspecific variation in longevity, which is comparable to that reported for the western honeybee. The average effective re- productive flight window of 10 days for A. flo- rea, is slightly more than half of the 18.8 days given for A. mellifera (Rueppell et al., 2005). The high correlation for the average num- ber of A. florea male flight days (9.2), relative

24 N. Buawangpang et al. to the mean flight window of 10 days, demon- strates that once a drone commences reproduc- tive flight there is a high probability of con- tinued flight until death. This would support a presumed fitness advantage for fast-maturing A. florea males as has been postulated for A. mellifera drones (Rueppell et al., 2005). The A. florea data on male flights per life- time, age at first flight, age at last flight, the re- productive flight window and total time spent in flight are the first to be reported for any Asian honeybee species. Tables I and II pro- vide the statistical summaries. Table I also compares our A. florea observations with those reported for A. mellifera.

Rueppell et al. (2005) working with A. mel- lifera, did find a highly significant correlation between the age of flight initiation and total number of days where mating flights were un- dertaken, which is contrary to our findings for A. florea. The regression analysis for the to- tal number of A. florea male flights vs. num- ber of flight days was however, highly signifi- cant (R2 = 0.93) and this is in agreement with earlier work on A. mellifera (Witherell, 1972). This is an intuitive correlation, i.e., longer lived males experience more flight days and hence more reproductive flights in their life- times.

Our data on drone longevity are based on the assumption that mortality is signified by a drone’s failure to return to its parent colony. The causes of the mortality are several and we have no way of discriminating between them, e.g., actual mating with a queen resulting in death; as a victim of any of several predatory entities; or physiological senescence. Drifting (mis-orientation) to another A. florea colony, while not resulting in death, would in our observations be considered mortality, even though those drones who do drift could the- oretically continue future mating flight from their new location.

The reproductive life history of A. florea males can be summarized as relative short and frenetic especially when compared to the only other honeybee species where such ob- servations are known (A. mellifera). Why such differences between A. florea and A. mellif- era drone flight behavior exist is speculative. A comparison of drone flight behavior be- tween the two species is one of a tropically adapted species relative to a temperate species, each observed in their own respective ecosys- tems. It would be illuminating to conduct a comparative study of the temperately adapted A. mellifera where it has been anthropogeni- cally placed in a tropical ecosystem as exists in northern Thailand. Further work on addi- tional Asian Apis species will be of interest in developing a deeper understanding of honey- bee drone reproductive behavior for the region of the world where Apis species diversity is at its greatest and where basic research stud- ies on male behavior have been conspicuously absent.

Le vol des mâles d’Apis florea : longévité et per- formance de vol. Apis florea / mâle / vol / longévité / performance Zusammenfassung – Der Drohnenflug bei Apis florea: Dauer und Flugleistungen. Bei der westli- chen Honigbiene Apis mellifera L. sind die Fluglei- stungen und das Verhalten beim Drohnenflug sehr gut untersucht. Wenig bekannt ist hingegen über das Drohnenflugverhalten bei den übrigen 8 Honigbie- nenarten der Gattung Apis, insbesondere bezüglich der altersabhängigen Flugaktivitäten und der Dau- er der Flüge. Da die Drohnen zu gleichen Teilen zur genetischen „Fitness“ eines Bienenvolkes bei- tragen, sind Untersuchungen zum Paarungssverhal- ten auch für ein besseres Verständnis der Repro- duktionsbiologie wichtig. In Südost-Asien ist dies von besonderem Interesse, da hier mehrere Honig- bienenarten sympatrisch vorkommen. In dieser Ar- beit werden weitere detaillierte Daten zum Droh- nenflug bei Apis florea F. vorgestellt, einer der zwei Arten von Zwerghonigbienen in Südost-Asien. Die Untersuchungen wurden an der Chiang Mai Univer- sität in Nord-Thailand während des Winters 2007 durchgeführt, zu einer Zeit in der viele Drohnen in den A. florea-Völkern gepflegt werden. Zur Be- obachtung des Drohnenfluges wurde ein schwarm- bereites A. florae-Volk auf den Universitätscampus transportiert. Um altersdefinierte Drohnen zu erhal- ten, wurde eine Wabe mit schlüpfender Drohnen- brut in einem Brutschrank mit 34 ◦ C und 75 % RF gehängt und die schlüpfenden Drohnen mit farbigen Nummernplättchen individuell markiert. Diese al- tersdefinierten Drohnen wurden dem A. florae-Volk zugegeben. Geschulte Beobachter beobachteten die Oberfläche des Bienenvolkes während der nachmit- täglichen Flugaktivitäten und erfassten Abflug- und Rückkehrzeitpunkt der markierten Drohnen. Die Beobachtungen wurden so lange fortgeführt, bis der letzte altersdefinierte Drohn nicht mehr zum Nest zurückkehrte.

Apis florea drone flight 25 Aus den Flugdaten von 42 Drohnen mit bekanntem Alter wurden die folgenden Mittelwerte berechnet: Alter beim ersten Flug, Alter beim letzten Flug, An- zahl an Flugtagen, Anzahl der Flüge eines Drohns, Dauer eines Paarungsfluges und der tägliche Zeit- raum für Drohnenflüge. Die Aufzeichnungen zu den Drohnenflügen sind in Abbildung 1 dargestellt. In Tabelle I werden die Mittelwerte für das Alter beim ersten Flug (5,6 Ta- ge), Alter beim letzten Flug (15,6 Tage), Anzahl Flüge pro Tag (9,1) und die Gesamtzahl an Flügen eines Drohns (15,3) zusammengefasst. In Tabelle I werden diese Parameter zusätzlich mit bekannten Daten von A. mellifera-Drohnen verglichen. Der durchschnittliche Paarungsflug von A. florea dauert 31 Min. und findet während eines Zeitraumes statt, der um ca. 12,00 beginnt und um ca. 14,00 endet. Von einer Gruppe von 20 altersdefinierten Drohnen, für die vollständige Aufzeichnungen vom ersten bis zum letzten Flug vorlagen, wurde eine mittlere Ge- samtflugzeit von 6h und 38 Min. berechnet, wo- bei es erhebliche Schwankungen gab. Die maximale Flugzeit für einen Drohn betrug 16 h und 51 Min., verteilt auf 39 Flüge an 25 Flugtagen. Da bisher wenig über die Flugleistungen bei den Drohnen der übrigen 7 asiatischen Apis-Arten be- kannt ist, verglichen wir unsere Beobachtungen an Drohnen von A. florea als eine an die Tropen ange- passte Bienenart mit den Drohnen einer an gemä- ßigte Klimate angepassten Art (A. mellifera). Auffällig ist zunächst die Ähnlichkeit bei der Länge des Paarungsfluges (ca. 30 Min. für beide Arten). Für die Anzahl an Flugtagen, das Alter beim ersten Flug sowie das Alter beim letzten Flug wurden für die Drohnen von A. florea dagegen deutlich gerin- gere Werte festgestellt. Im Vergleich zu A. melli- fera kann die Flugaktivität von A. florea-Drohnen daher als „kurz und heftig“ zusammengefasst wer- den. Sinnvoller wäre allerdings ein Vergleich mit der Drohnenflugcharakteristik von anderen sympa- trischen Apis Arten in Südost-Asien; allerdings wä- ren hierfür mehr Forschungen an diesen Bienenar- ten notwendig.

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